Moulding compositions including an unsaturated polyester

ABSTRACT

Molding composition comprising from 10 to 50 wt.% of the polycondensation product of 2,2&#39;-bis(4-hydroxycyclohexyl) propane or a halogenated derivative thereof, and maleic or fumaric acid, having a melting point above 70° C, an acid value of less than 50 and a Gardener viscosity from Y to Z 3 , from 0.2 to 2 wt.% of an organic peroxide which decomposes at a temperature above 70° C, and an inert filler. 
     The resulting molded articles are particularly useful in the electrical and electronic fields.

The present invention concerns moulding compositions including anunsaturated polyester and the moulded articles manufactured from thesaid compositions.

Unsaturated polyester resins consisting of the products of thepolycondensation of unsaturated polybasic acids with polyvalentalcohols, in solution in styrene or another unsaturated liquid monomerare known in the art.

The said resins harden under the action of catalysts such as the organicperoxides, possibly used in conjunction with polymerization accelerants,such as, for example, cobalt naphthenate or octoate.

The unsaturated polyester resins find their main use in combination withreinforcers of a fibrous nature, for preparing manufactured articlescommonly known as "reinforced plastics".

The reinforcers commonly used for the purpose are: asbestos, cotton,jute and especially glass, in fibre or fabric form.

Various methods for moulding reinforced unsaturated polyester resins areknown, which generally consist of arranging a fibrous reinforcer in asuitable mould into which the liquid resin containing the catalyst forhardening is poured, or else the said resin is sucked or injected intothe mould. The resin is then hardened at high temperature, possiblyunder pressure.

Examples of these methods are: direct compression moulding, moulding bysuction and injection moulding.

Also known is direct moulding with preforming, which consists ofsubjecting to moulding a "preform", made of glass fibre impregnated withresin and formed by suction in a suitable chamber, and by thermaltreatment of the said deposited material in a current of air.

These processes are somewhat onerous and do not allow high productivityof the moulded objects. The said moulded objects have, moreover, variousundesirable characteristics, such as, for example, the small of theunsaturated monomer used in the resin in combination with thepolycondensation products of the unsaturated polybasic acids with thepolyhydroxy alcohols. Finally, there are various difficulties inhandling substances such as unsaturated polyester resins.

The thermoplastic resins, unlike the thermosetting ones, are mouldedwith great ease and speed, in apparatus in which they are firstuniformly heated to fluidity and then injected into a mould in whichhardening takes place.

The application of such a method to the thermosetting resins involveshaving available moulding compositions, comprising the thermosettingresin, a hardening catalyst, and an inert filler, possessing thefollowing characteristics:

-- stability in storage for long periods of time at ambienttemperatures;

-- ability to change into the fluid state within temperature limits inwhich the phenomenae of premature cross-linking and hardening do notoccur appreciably;

-- ability to harden rapidly at temperatures higher than those necessaryto ensure fluidity of the mass.

Preferably these moulding compositions should be in the form of easilyflowing granules having no tendency to release dust.

No moulding compositions, including an unsaturated polyester resin,possessing all the characteristics listed above are known.

Moulding compositions have now been found including an unsaturatedpolyester, a hardening catalyst and an inert filler, which are stable atambient temperature, fluid within temperature limits in which prematurecross-linking and hardening do not occur, and which harden rapidly athigh temperatures.

The said compositions, in flowing granular form, free from the tendencyto release dust, are converted into moulded articles by known methods,including injection moulding, in the same way as thermoplasticmaterials.

The moulded articles thus obtained have an unusual combination ofcharacteristics.

Thus, the invention provides a moulding composition comprising:

a. from 10 to 50% by weight of on unsaturated polyester consisting ofthe polycondensation product of a polyhydroxy alcohol chosen from2,2'-bis(4-hydroxycyclohexyl)propane and its halogenated derivatives,and an ethylenically unsaturated dicarboxylic acid chosen from maleicand fumaric acids, having the following characteristics:

-- melting point (at the capillary) > 70° C

-- acid value (mg KOH/g) < 50

-- Gardner viscosity (at 25° C in 60 wt.% solution in styrene): from Yto Z₃

b. from 0.2 to 2% by weight of an organic peroxide which decomposes at atemperature above 70° C;

c. at least one inert filler.

In addition to the polycondensation product, the peroxide and thefillers, the moulding composition may also contain small amounts ofconventional additives, such as polymerization inhibitors, lubricants,dyes and pigments.

Unsaturated polyester

The unsaturated polyester useful for the purposes of the presentinvention is the product of the polycondensation of2,2'-bis(4-hydroxycyclohexyl) propane, or a halogenated derivativethereof, and an ethylenically unsaturated dicarboxylic acid, chosen fromfumaric acid and maleic acid, having moreover the following generalcharacteristics:

-- melting point > 70° C

-- acid value < 50

-- Gardner viscosity: from Y to Z₃

where: the melting point is determined by the capillary method, the acidvalue is the number of milligrams of potassium hydroxide necessary toneutralize one gram of unsaturated polyester, and the viscosity isdetermined at 25° C in 60% solution by weight of the unsaturatedpolyester in styrene.

It should be noted that by halogenated derivatives of 2,2'-bis(4-hydroxycyclohexyl) propane are meant the chloro- or bromo-derivatives, in the ring and/or in the propane radical.

The unsaturated polyester which is preferred for the purposes of thisinvention has general characteristics in the following ranges of values:

-- melting point: from 80° to 95° C

-- acid value: from 15 to 20

-- Gardner viscosity: from Z₁ to Z₃

Preparation of the unsaturated polyester

2,2'-bis(4-hydroxycyclohexyl)propane, or a halogenated derivativethereof, and the unsaturated dicarboxylic acid, are placed in contact ina molar ratio of from 1.05:1 to 1.1:1 and polycondensed at elevatedtemperature, while removing the water which forms in the reaction, untilthe preselected acid value of the unsaturated polyester is reached.

According to a preferred embodiment the reaction is carried out at atemperature of from about 190° to about 210° C, the water being removedinitially at atmospheric pressure until the acid value of theunsaturated polyester is from about 40 to about 50, and then atsub-atmospheric pressure (e.g. 10-50 mm Hg) until the desired acid valueis reached.

The best results are obtained with a molar ratio of2,2'-bis(4-hydroxycyclohexyl) propane, or its halogenated derivative, tothe unsaturated polycarboxylic acid of the order of 1.1:1.

The moulding compositions

The composition of this invention preferably contains from 20 to 35% byweight of unsaturated polyester and from 0.5 to 1.8% by weight oforganic peroxide.

The organic peroxide has preferably a decomposition temperature higherthan 120° C.

Examples of organic peroxides suitable for the purposes of the inventionare:

-- dialkyl peroxides, such as di-tert-butyl peroxide;

-- diaralkyl peroxides, such as dicumyl peroxide;

-- cyclic peroxides, such as dibenzylidene diperoxide;

-- peroxy esters, such as tert-butyl peroxybenzoate and di-tert-butylperphthalate;

-- peroxides of the ketal type, e.g. that known commercially as"Trigonox 17/40" .

The latter is used in combination with known polymerization accelerants,such as the cobalt, manganese, cerium, nickel and iron salts of organicacids and particularly cobalt naphthenate and octoate.

The inert fillers are preferably silica, calcium carbonate, asbestos andglass fibre. The latter is generally present in the composition inamounts of from 10 to 55% by weight, preferably in the form of fibres ofthe order of 3-10 mm in length.

The composition of the present invention generally contains from 20 to500 ppm (with respect to the unsaturated polyester) of one or moresubstances chosen from among those conventionally used in the art toinhibit polymerization of the unsaturated polyester resins.

These inhibitors can be chosen from wide set of compounds, such as:quaternary ammonium salts, salts of amines, salts of copper,nitrophenols, dihydric phenols and their alkyl derivatives.

The moulding composition generally contains from 1 to 3% by weight of alubricant preferably chosen from waxes, stearic acid and zinc, calciumand magnesium stearates. Further additives generally present in thecomposition are dyes and pigments.

Preparation of the moulding composition

The moulding composition of the present invention may be prepared in thefollowing way. All the components except the glass fibre are fed into aball mill and ground to a grain size of the solid of less than about 100microns. Then the glass fibre is added, the mass is homogenized in apowder mixer, operating in conditions such that the glass fibre will notbe broken, and the homogenized mass is calendered, operating for timesof the order of a few minutes and with roller temperatures not aboveabout 100° C, until a sheet of thickness of the order of 1 mm isobtained. This latter is ground, e.g. in a hammer mill, and theresulting granules are sifted in order to separate the fraction havingthe desired grain size. A moulding composition in the form of granulesfrom 100 to 5000 microns, is thus obtained. Absence of particles withdimensions less than 100 microns is preferable, or, at least, suchparticles should not exceed 5% by weight of the composition.

According to another procedure, after homogenisation with the glassfibre, the composition is extruded, and the granulate is obtained bymeans of "in-head cutting" of the extrudate.

The composition is stable at ambient temperatures for a period of timegreater than three months and generally up to six months, especially ifkept in watertight bags, e.g. of polythene or polythene paper. Storagetemperatures below the ambient temperature cause no damage. Moreover thesaid composition has no tendency to release dust.

The compositions become fluid and flowing at temperatures in the rangeof from 120° to 130° C and at these temperatures they have a "plasticlife" or useful time for processing greater than 125 seconds up to 15minutes or more.

Hardening occurs at a temperature of from 145° to 180° C, in a time ofthe order of from 100 to 10 seconds.

The data resulting to the "plastic life" and to the hardening speed weredetermined by means of the Brabender rheometer from BrabenderInstruments Inc.

More particularly the said rheometer comprises a cell with a device withrotors which can rotate at different speeds. The whole system isthermostatted.

The moulding composition is fed into the cell. Under the action of thetemperature and the friction of the rotors, the composition undergoesboth physical and chemical changes.

The resistance with which the composition opposes the action of therotors, expressed as a turning moment in revolutions per minute, ismeasured and recorded as a function of time.

It is thus possible to determine the softening, melting and hardeningcycles of the composition under examination, obtaining useful data forinjection moulding.

Preparation of moulded articles

Preparation of the moulded articles can be effected by normal methods ofcompression, transfer and injection moulding, using moulding cycleswhich are speedy and completely automatic.

In direct compression moulding the mould can be filled at pressure offrom 12 to 250 Kg/cm², especially depending on the geometry of thearticle, with optimal moulding temperatures of from 145° to 165° C.

In "transfer" moulding the best results are obtained with directlyincorporated chamber moulds, with the feed heads as short as possibleand with a single injection per cavity. Moulding temperatures are of theorder of 145°-155° C.

The best results are achieved by injection moulding in which themoulding composition is made fluid by screw-type extrusion and theninjected into the mould where it undergoes hardening.

In each case hardening occurs without generation of gaseous by-products.

The resulting moulded articles have a great dimensional stability atelevated temperature, exceptionally low shrinkage values, and excellentelectrical properties which remain unchanged under differentenvironmental conditions.

The said moulded articles possess, moreover, good mechanicalcharacteristics, very good resistance to chemical reagents, and,especially if halogenated, high flame resistance. They have also a lowwater absorption and can easily be coloured.

In particular, the said moulded articles possess electricalcharacteristics similar to those of conventional products used for thepurpose, such as glass and ceramics, the said characteristics beingdistinctly superior to those of products manufactured from thermosettingresins such as phenol, urea and melamine resins, and also to thosemanufactured from the usual thermoplastic resins.

The manufactured articles of the present invention moreover, showdistortion temperatures under load (Martens degree) clearly superior tothose made from the conventional thermoplastic resins.

In conclusion, the moulded articles of the present invention possess awhole collection of characteristics such as to render them useful in awide range of applications and particularly for the construction ofelectrical and electronic equipment parts, such as: reels for coils,boxes for low and medium tension switches, insulators in general,connector blocks, fairleads, terminals, handles, insulating supports andfans for electric motors.

EXAMPLE Preparation of the unsaturated polyester

Into a distillation flask fitted with an agitator there are fed 264.4parts by weight of 2,2'-bis(4-hydroxycyclohexyl) propane and 116 partsby weight of fumaric acid, the molar ratio between the two reagentsbeing of 1.1:1.

A current of nitrogen is caused to flow over the surface and thereagents are melted by heating to 170°-180° C.

They are then heated to 200°-205° C whilst the temperature is maintainedat the swan neck at about 105° C.

The said temperatures are maintained until an acid value of the order of40-50 is reached.

A subatmospheric pressure (20 mm Hg) is then applied and the temperatureis maintained at 200°-205° C until an acid value of the polyester resinof less than 20 is reached.

100 ppm of para-tert-butyl catechol are added, the mass is cooled anddischarged.

The unsaturated polyester thus obtained has the followingcharacteristics:

-- melting point: 91° C

-- acid value: 17.6

-- Gardner viscosity: Z₂ + 1/2

The melting point is determined in a capillary; the acid value indicatesthe milligrammes of potassium hydroxide used to neutralize 1 gram ofunsaturated polyester; the Gardner viscosity is determined at 25° C in60% solution by weight of the unsaturated polyester in styrene.

Preparation of the moulding composition

A moulding composition including the unsaturated polyester thus obtainedis prepared.

In particular, the said composition is formed from:

-- unsaturated polyester : 34.0% by weight

-- tert-butyl perbenzoate : 1.6% by weight

-- silica : 5.0% by weight

-- zinc stearate : 2.5% by weight

-- calcium carbonate : 26.9% by weight

-- glass fibre (chopped strands) : 30.0% by weight

The silica used is that known commercially as "Aerosil".

The preparation of the composition is carried out in the followingmanner:

all the components, excepting the glass fibre, are fed into a ball milland ground to a grain size of less than about 100 micron.

Then the glass fibre is added and the mass is homogenized.

The homogenized mass is calendered, working under the followingconditions:

-- first roller temperature : 100° C

-- second roller temperature : 85° C

-- speed of the two rollers : 20 revolutions/minute

-- working time : 2 minutes

-- thickness of the sheet produced: 1 mm

The sheets produced by calendering are ground in a hammer mill, having anet with a 5 mm mesh.

The granulate obtained has the following characteristics:

-- apparent density : 700 g/l

-- hardening time at 150° C : 120 seconds

-- flow index at 150°0 C : 7 seconds

-- fluidity on a disc : 7.5

-- stability in storage: more than 3 months

-- packing: a little friable

-- grain size (micron)

4000 2-5%

1250 60-63%

500 25-27%

250 5-7%

100 3-4%

<100 3-4%

Under the moulding conditions, the granulate does not adhere to thewalls of the chromium plated moulds, and moreover it is not necessary tolubricate the said moulds.

It should be noted that in the foregoing determinations:

-- the apparent density was determined in accordance with the DIN 53.468standard;

-- the hardening time was determined by introducing the composition intoa bowl shaped mould of the UNI 4272 type and putting it under a load of5,000 Kg., at a temperature of 150° C; the time in seconds elapsingbetween the closing of the mould and the formation of a bowl withoutsurface defects (blisters) defines the hardening time;

-- the flow index was determined by introducing the composition into abowl shaped mould of the UNI 4272 type, at the prefixed temperature of150° C and applying a load of 5,800 Kg. by means of a hydraulic press;at the instant at which the needle of the manometer, connected to thepress, shows an increase in pressure, the chronometer is started; whenthe upper plane of the press has finished its descent, the chronometeris stopped; the intervening time, expressed in seconds, is the flowindex;

-- fluidity on a disc was determined by placing 50 grams of thecomposition at the centre of a disc-shaped mould, having a diameter of32 cm and with 6 concentric circles drawn on the said mould; a pressureof 40,000 Kg is applied for 60 seconds operating at 150° C; the speed ofclosing of the press is at 0.3 cm/second; the fluidity of thecomposition is expressed as the number of circles impressed on the disc;

-- packing was estimated by placing 100 grams of the composition in a250 ml beaker with a 66 mm inner diameter under a pressure of 15.1 g/cm²; after 45 days at 38° C the composition is sifted through sieves of 20,40 and 50 mesh and the quantity of material remaining on each sieve aswell as the consistency of the lumps is evaluated; the handlingconsistency of the lumps is expressed by the words: non friable, alittle friable, friable.

Characteristics of the moulded products

Test bars are moulded, with dimensions 10 × 15 × 120 mm, following UNIstandards and under the following moulding conditions:

-- temprature : 160 ± 2° C

-- pressure : 200 Kg/cm²

-- time : 90 seconds/mm thickness

The following characteristics of the test pieces were determined:

-- bending strength DIN 53452 (Kg/cm²): 510

-- impact strength DIN 53453 (Kg.cm/cm²): 4.2

-- impact strength with notch DIN 53453 (Kg.cm/cm²): 3.7

-- Martens degree DIN 53458 (° C): 140

-- shrinkage DIN 53464 (%): 0.69

-- post-shrinkage DIN 53464 (%): 0.08

-- water absorption DIN 53472 (mg): 21

-- surface resistivity DIN 53482 (ohm): 6 10¹⁴

-- volume resistivity DIN 53482 (ohm.cm): 3 10¹⁵

-- dissipation factor DIN 53483 (tang δ ): 0.019

-- dielectric strength DIN 53481 (Kv/mm): 4.8

-- tracking resistance DIN 53480 (degree): KA3c

-- degree of incandescence DIN 53459 (degree): 2

We claim:
 1. A granular molding composition suitable for injectionmolding comprising:a. from 10 to 50% by weight of an unsaturatedpolyester consisting of the polycondensation product of a polyhydroxyalcohol selected from the group consisting of2,2'-bis(4-hydroxycyclohexyl) propane and its halogenated derivatives,and an ethylenically unsaturated dicarboxylic acid selected from thegroup consisting of maleic and fumaric acids, having the followingcharacteristics:-- melting point (at the capillary) > 70° C -- acidvalue (mg KOH/g) < 50 -- Gardner viscosity (at 25° C in 60 wt.% solutionin styrene): from Y to Z₃ b. from 0.2 to 2% by weight of an organicperoxide which decomposes at a temperature above 70° C; c. one or moreinert fillers.
 2. The molding composition of claim 1, which comprisesfrom 20 to 35% by weight of said unsaturated polyester and from 0.5 to1.8% by weight of said organic peroxide.
 3. The molding composition ofclaim 1, in which said unsaturated polyester has the followingcharacteristics:-- melting point from 80° to 95° C -- acid value from 15to 20 -- Gardner viscosity from Z₁ to Z₃.
 4. The molding composition ofclaim 1, in which said inorganic peroxide has a decompositiontemperature above 120° C.
 5. The molding composition of claim 1, inwhich said organic peroxide is selected from the group consisting ofdialkyl peroxides, diaralkyl peroxides, cyclic peroxides, peroxyestersand peroxides of the ketal type.
 6. The molding composition of claim 1,in which said organic peroxide is selected from the group consisting ofdi-tert-butyl peroxide, dicumyl peroxide, dibenzylidene diperoxide,tert-butyl peroxybenzoate and di-tert-butyl perphthalate.
 7. The moldingcomposition of claim 1, in which said inert filler is selected from thegroup consisting of silica, calcium carbonate, asbestos and glass fiber.8. The molding composition of claim 1, which comprises from 10 to 55% byweight of glass fiber as inert filler.
 9. The molding composition ofclaim 1, which comprises from 20 to 500 ppm with respect to saidunsaturated polyester, of a polymerization inhibitor selected from thegroup consisting of quaternary ammonium salts, salts of amines, salts ofcopper, nitrophenols, dihydric phenols and their alkyl derivatives. 10.The molding composition of claim 1, which comprises from 1 to 3% byweight of a lubricant selected from the group consisting of waxes,stearic acid and stearates of zinc, calcium and magnesium.